Description

The lgrp_latency_cookie() function takes a cookie representing a snapshot of the lgroup
hierarchy obtained from lgrp_init(3LGRP) and returns the latency value between a hardware resource
in the from lgroup to a hardware resource in the to lgroup.
If from is the same lgroup as to, the latency value within
that lgroup is returned.

The between argument should be set to the following value to specify
between which hardware resources the latency should be measured:

LGRP_LAT_CPU_TO_MEM /* latency from CPU to memory */

The latency value is defined by the operating system and is platform-specific.
It can be used only for relative comparison of lgroups on the
running system. It does not necessarily represent the actual latency between hardware
devices, and it might not be applicable across platforms.

The lgrp_latency() function is similiar to the lgrp_latency_cookie() function, but returns the
latency between the given lgroups at the given instant in time. Since
lgroups can be freed and reallocated, this function might not be able
to provide a consistent answer across calls. For that reason, the lgrp_latency_cookie() function
should be used in its place.

Return Values

Upon successful completion, the latency value is returned. Otherwise -1 is returned
and errno is set to indicate the error.

Errors

The lgrp_latency_cookie() and lgrp_latency() functions will fail if:

EINVAL

The specified cookie, lgroup ID, or value given for the between argument is not valid.

ESRCH

The specified lgroup ID was not found, the from lgroup does not contain any CPUs, or the to lgroup does not have any memory.